<title>Logical AND OR and NOT</title>
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<h1>Logical AND OR and NOT</h1>
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<ul>
<li><a href=#AND>Logical AND is &&</a>
<li><a href=#OR>Logical OR is ||</a>
<li><a href=#NOT>Logical NOT is !</a>
</ul>
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<a name=AND>
<h2>Logical AND</h2>
In simple terms, && is true (1) if both sides of the expression returns NOT 0.
<p>
For Example:
<pre>
	/* These all return TRUE (1) */

	if (4 && 5) return();

	i=3;
	j=2;
	return( i && j);
</pre>
The expression is evaluated 'Left to Right' If any part of the expression 
returns ZERO - The evaluation ends. 
<p>
THIS CAN CAUSE SERIOUS PROBLEMS.
<p>
For example:
<pre>
	k=0;
	i=3;
	j=2;
	if ( i-i && j++) k=1
</pre>
The left side <i>(i-i)</i> resolves to 0, so <i>j</i> is not incremented 
and <i>k</i> is not changed. 
<hr>
<a name=OR>
<h2>Logical OR</h2>
OR also evaluates 'Left to Right' and will stop when an expression 
returns true. <p>
SO WATCH YOUR BACK....
<p>
<pre>
	k=0;
	i=3;
	j=2;
	if ( i+i && j++) k=1
</pre>
What are <i>j</i> and <i>k</i> going to be when this code is executed?????

<hr>
<a name=NOT>
<h2>Logical NOT</h2>

NOT reverses the logical state of its 
<a href=../glossary.html#operand>operand</a>. If the operand is 0, 1 is 
returned, else 0 is returned.

<pre>
	!4	/* Returns 0	*/
	!-4	/* Returns 0	*/
	!1	/* Returns 0	*/
	!0	/* Returns 1	*/
</pre>


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<address><a href="../../address.html">Martin Leslie</a> 
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